Increased channel capacity is a very desirable goal as indicated by the cellular and personal communication service providers. With available spectrum limiting channel capacity, cellular service providers quickly reach maximum usage in a given system. Since the conventional cellular systems limit the number of users on the same channel at a time, it is very desirable to design an antenna system that can handle multiple users on the same frequency at the same time, and thus, increase the capacity of each channel. Co-channel interference is another serious technical problem in cellular radio. Co-channel interference, which is caused by interference from other users operating at the same frequency as the designated user, is increased in a multipath environment. Due to the presence of co-channel interference, the quality of the received signals is degraded substantially. There is therefore a need to improve cancellation of co-channel interference.
There are known antennas, referred to as corner reflector antennas, which employ a radiating element mounted adjacent to the corner of a pair of intersecting reflecting surfaces provides a directional radiation pattern in azimuth. In some applications, a number of corner reflector antennas have been put together to enhance the antenna gain of the overall system. A corner reflector [such as described in The Corner-Reflector Antenna, John D. Kraus, Proceedings of the I.R.E., November 1940, p. 513-519] uses a dipole located parallel with two planes that intersect each other with an angle of 90.degree.. One can use any angle that is 360.degree./n, where n is an even integer. One can make n=2 and a plane reflector results, or n=4 where .theta.=90.degree. (the usual case), and a right angle corner reflector results, or n=6 where .theta.=60.degree. (somewhat higher gain than the usual case if the two reflecting sheets are large enough). Normally, n values of 8 or larger do not produce a practical antenna with respect to size, gain and input impedance. Woodward [U.S. Pat. No. 2,897,496 issued July 1959] has shown how one can put various driven elements into the antenna, such as center-fed conductors attached to the two conducting sheets, tilted dipoles and square cross-sectional helices. Inagaki [Three-Dimensional Corner Reflector Antenna, Naoki Inagaki, IEEE Transactions on Antennas and Propagation, July, 1974, p. 580-582] and Elkamchouchi [Cylindrical and Three-Dimensional Corner Reflector Antennas, Hassan M. Elkamchouchi, IEEE Transactions on Antennas and Propagation, vol. AP-31, No. 3, May, 1983, p. 45-455] treat the case of adding a third plane to the antenna to obtain a three-dimensional corner reflector antenna. Klopfenstein [Corner Reflector Antennas with Arbitrary Dipole Orientation and Apex Angle, Ralph W. Klopfenstein, I.R.E. Transactions on Antennas and Propagation, July, 1957, p. 297-305] has also considered the corner reflector with arbitrary angles as well as an arbitrary dipole orientation.
Kommrusch [U.S. Pat. No. 4,101,901 issued July 1978], Davidson [U.S. Pat. No. 4,213,132 issued July 1980] and Stimple [U.S. Pat. No. 4,170,759 issued October 1979] use multiple corner reflector antennas for interleaved beams, multiple frequency inputs, and a switched antenna arrangement respectively. In these devices, a fixed splitting and coupling arrangement connects the transmitters or receivers to the multiple antennas. Franke [U.S. Pat. No. 4,983,988 issued January. 1991] also uses a multiple (4 element) corner reflector for a cellular radio application. All of these multiple corner reflector antennas have good isolation between antennas. Another type of sectored antenna is described by Bitter [U.S. Pat. No. 5,185,611 issued February 1993]. Three antennas are built into a single structure and the design provides good isolation between the elemental antennas. Yet another type of multiple antenna is described by Chu [U.S. Pat. No. 5,654,724 issued August 1997]. This arrangement uses four half loops mounted over a ground plane. These loops are connected to splitters in a fixed arrangement to the transmitter and receiver. The inter-element isolation in this antenna is achieved primarily by the spatial separation of the loops.